Computer graphics systems represent graphical primitives as pixel elements of a display. Aliasing refers to the visual artifacts, such as stair-stepping of surface edges (sometimes known as “jaggies”), that occur when an image is sampled at a spatial sample frequency that is too low.
A variety of anti-aliasing techniques exist to reduce visual artifacts. One example is supersampling, in which an image is sampled more than once per pixel grid cell and the samples are filtered. For example, in supersampling, the contribution of each sample in a pixel may be weighted to determine attributes of the pixel, such as the pixel color. Another example of an anti-aliasing technique is multisampling. As objects are rendered in a multisampling system, a single color is typically computed per primitive and used for all subpixel samples covered by the primitive.
In both supersampling and multisampling, the quality of the anti-aliasing tends to improve as the number of samples per partially covered pixel increases. For example, increasing the number of samples per pixel from four samples (“4×” sampling) to sixteen samples (“16×” sampling) would be expected to reduce visual artifacts. However, as the number of samples per pixel increases, more sample data must be generated, stored, transported and processed. Consequently, more computing resources, such as memory and bandwidth, may be needed as the number of samples per pixel is increased. As a result, the cost and complexity of graphics systems tend to increase as the number of samples used for anti-aliasing increases.